Method and composition for reducing the frictional drag of flowing fluids

ABSTRACT

THE FLOW PROPERTIES OF NON-AQUEOUS LIQUIDS ARE IMPROVED BY THE INCORPORATION THEREINTO OF HYROGENATED POLYISOPRENE.

n aastates Patent Olive 3,801,508 Patented Apr. 2, 1974 3,801,508 METHOD AND COMPOSITION FOR REDUCING THE FRICTIONAL DRAG OF FLOWING FLUIDS Dale J. Meier, El Cerrito, Calif., and Vitold R. Kruka, Houston, Tex., assignors to Shell Oil Company, New York, NY. No Drawing. Filed Dec. 2, 1971, Ser. No. 204,357

Int. Cl. Cm 1/18 U.S. Cl. 252-59 1 Claim ABSTRACT OF THE DISCLOSURE The flow properties of non-aqueous liquids are improved by the incorporation thereinto of hydrogenated polyisoprene.

BACKGROUND OF THE INVENTION In the transferral of liquids by fluid flow it is well known that energy is required to overcome friction encountered in the movement of the liquid. When a fluid is pumped or transferred under pressure, the frictional loss is apparent as a pressure drop along the pipe or conduit in which the liquid is being transferred. Pressure drops such as these are generally large under conditions where the velocity of the liquid exceeds the critical limit for laminar flow. High frictional losses characteristically accompanying non-laminar flow generally occur in industrial operations wherein high fluid velocities are necessary, for example in the movement of large volumes of fluid over great distances such as in petroleum pipelines.

Considerable amounts of energy must necessarily be expended to compensate for the pressure drops caused by such friction loss. Therefore, it is manifest that a reduction in such friction loss would result in lowering operating pressures and in return would reduce power requirements. Likewise, using the same power input, increased flow rates could be achieved.

The addition of various materials as friction reducers has been proposed in the prior art. For example, the effectiveness of cis-polyisoprene as a friction reducing agent is brought out in U.S. Pats. 3,215,154 and 3,493,000. While polyisoprene is indeed an excellent friction reducing agent, as demonstrated by these two patents, hydrogenated polyisoprene is an even better friction reducing agent as will be shown hereinafter.

The use of ethylene-propylene copolymer is also known as a friction loss reduction additive as shown in U.S. Pats. 3,351,079 and 3,493,000. Ethylene-propylene copolymer bears resemblance to hydrogenated polyisoprene in that both appear to be copolymers of ethylene and propylene. The chief difference between the two polymers resides in structure. Thus, if A represents ethylene monomer and B propylene monomer, the units A and B in a hydrogenated polyisoprene molecule are arranged alternatievly, e.g., A-B-A-B-A-B-A-B-. By comparison, in the ethylenepropylene copolymer the units A and B can be arranged at random, e.g., A-B-A-A-B-A-B-B-, or in blocks, A-A- B-B-A-A-B-B-B-B-. This difference has a profound effect on properties and the superiority of the hydrogenated polyisoprene to the ethylene-propylene copolymer will be shown hereinafter.

The present invention provides a successful and improved solution to the above noted problem of the prior art, as well be apparent from the following description thereof.

SUMMARY OF THE INVENTION The primary purpose of this invention resides in providing a composition and method for the reduction of friction loss in flowing non-aqueous fluids, which composition and method are superior to others in the prior art.

The above purpose has been achieved through the utilization of hydrogenated polyisoprene as a friction loss additive.

The composition of this invention broadly extends to a non-aqueous liquid medium having dispersed therein from about 1 p.p.m. to aobut 2,000 p.p.m. of hydrogenated polyisoprene.

The method of this invention broadly extends to reducing fluid flow friction loss in the transfer of a nonaqueous liquid medium through a piper or conduit which involves intermixing with the medium from about 1 p.p.m. to about 2,000 p.p.m. of hydrogenated polyisoprene and flowing the intermixed medium and hydrogenated polyisoprene through the pipe or conduit.

Within the framework of the above described method and composition, the present invention not only solves the above mentioned problem of the prior art, but also achieves further significant advantages as will be apparent from the description of preferred embodiments following.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the teachings of the present invention, the above purpose is achieved by adding to the non-aqueous fluid to be transferred small amounts of hydrogenated polyisoprene. This polymer, which is soluble in a large number of non-aqueous fluids at the concentrations which are desired, has been found to reduce friction loss by as much as 27% when present in quantities as low as 2 p.p.m. based on a non-aqueous fluid, or 45% reduction with 11 p.p.m. concentration. These representative values vary based on the average molecular weight of the polymer, flow conditions and solvent power of the fluid.

The non-aqueous liquids incorporated by the invention especially include hydrocarbon liquids such as crude oil and fractions thereof, it being understood that the present invention is particularly adapted to reducing friction loss in the transportation of crude oil through great distances in a pipeline. However, the problem of high friction loss caused by non-laminar flow is frequently met in a variety of industrial operations involving other non-aqueous fluids wherein use of the present invention is particularly desirable and beneficial.

Hydrogenated polyisoprene has been prepared commercially for some time by a number of processes well known in the art, for example see the following U.S. Patents relating to hydrogenation: 2,693,461, 3,113,986, 2,093,096, 2,046,160, 3,130,237. Chemically, the completely hydrogenated polymer is a long chain linear hydrocarbon consisting of the following repeating units:

The hydrogenation need not be carried to completion and hydrogenation levels between 50 and are broadly suitable for the present usage. The use of complete hydrogenation gives the polymer better shear stability and solubility characteristics while partial hydrogenation appears to only give better solubility characteristics compared to polyisoprene.

While significant reductions in frictional losses are ob served with the addition of hydrogenated polyisoprene having a viscosity average molecular weight lower than 1x10 it is preferable that the polymer have a viscosity average molecular weight in the range of from about especially perferred that the polymer have a viscosity average molecular weight in the range of from about 1 10 to 2X10".

It is preferred that the hydrogenated polyisoprene for use with this invention predominantly be hydrogenated 1,4-polyisoprene For example, a hydrogenated polyisoprene found particularly effective is approximately 92% cis 1,4; 4% trans 1,4 and 4% 3,4; or, althogether, about 96% 1,4 polyisoprene.

Hydrogenated polyisoprene affords effective friction reduction when present in concentrations as low as 1 p.p.m., and under some conditions may afford worthwhile reductions at even lower concentrations although it is generally preferred that the polymer be present in higher concentrations. While the polymer may be persent in concentrations greater than 2,000 parts per million, it is generally not necessary to use such high concentrations. Accordingly, a range of from about 1 p.p.m. to about 2,000 p.p.m. is preferred for use with the invention. Of course, the optimum amount of polymer will vary depending on the molecular weight of the polymer and the flow conditions of the liquid. Generally, appreciable and economical reduction in friction loss under conditions of turbulent flow may be had with very little hydrogenated polyisoprene.

Usually, the presence of the polymer in the non-aqueous liquid in small amounts does not affect the eventual use of the non-aqueous liquid. However, it is feasible to remove the polymer from the fluid onceits purpose has been served although this is not generally economical.

Pursuant to practice of the present invention, the hygenerated polyisoprene may be intermixed directly with the non-aqueous fluid as a solid. Alternatively, an additive concentrate may be prepared by dissolving the polymer is kerosene or other suitable liquid. In order to increase the rate of solution, the concentrate mixture can be heated up to 200 F. without serious detrimental effect on subsequent friction loss reduction. Higher temperatures may cause problems since hydrogenated polyisoprene is known to decompose at temperatures above about 620 F. even in the absence of oxygen.

The following examples are presented to demonstrate the improvements of the invention and are not intended as limiting thereof. Thus, as will be shown hereinafter, hydrogenated polyisoprene is more shear stable than polyisoprene. Shear stability of polymer additives is beneficial whenever such additives are subjected to shearing forces, for example as friction reduction agents, lube oil additives, and wax improvers. Also as will be shown hereinafter, hydrogenated polyisoprene is more readily dissolved in hydrocarbon liquids than ethylene-propylene copolymer. Ease of dissolution is of critical importance in view of its effect upon the economy of the process.

EXAMPLE I The superior shear stability of a hydrogenated sample of cis-polyisoprene was tested and compared with its nonhydrogenated polyisoprene precursor. Both samples had a weight average molecular weight of 400,000 and both samples were tested at a concentration of 400 p.p.m. in cyclohexane. The test system consisted of a 4-foot long 0.143-inch I.D. glass tube with pressure taps located 7 inches apart in the fully developed portion of the flow. The sample solution was circulated through the system by means of two -inch diameter pistons at the opposing ends of the'glass tube. This method of pumping the solutions eliminated the high intensity shear degradation of the polymers which takes place in conventional pumps, especially centrifugal pumps.

The solutions were recirculated through the flow system at a wall shear stress of 6000 dynes/cm. The wall shear stress is givn by where D is the pipe diameter and dp/dx the pressure gradient. The IESIJIi-S; shown in Table I, are reported in terms Hydrogenated Number of passes Polyisoprene polyisoprene As can be seen, the hydrogenated sample not only gives. a greater amount of friction reduction initially than the polyisoprene but also does not lose its ability to do so after 600 passes through the system. The polyisoprene sample shows a significant loss of friction reducing abil-' ity after 600 passes.

Percent friction reduction is known to be very sensitiveto the molecular weight of the polymer. For instance, a 250 p.p.m. concentration in cyclohexane of an 8.2. 10 molecular weight polyisobutylene was found to yield a 21.1% friction reduction while under the same conditions a 1.83 10 molecular weight polyisobutylene was found to yield 57.2% friction reduction. Thus the loss of friction reducing ability with time or number of passes through a flow system is due to degradation of the polymer molecules.

EXAMPLE II To compare rates of dissolution of the hydrogenated polyisoprene to those of copolymers of ethylene-propyb ene, 1.5 gm. samples of each were placed in 200 cc.s of cyclohexane and a West Texas crude oil. Beakers containing the polymer, solvent and a magnetic bob were placed on magnetic stirrers operating at approximately 60 r.p.m. to provide gentle stirring to facilitate dissolution. The dissolution was allowed to proceed at room temperature. The polymers were deemed to have been completely dissolved when the solution appeared optically homogeneous and/or passed a fine mesh filter. The two polymers in this instance were a hydrogenated polyisoprene with an intrinsic viscosity of 6.85 dl./gm. at 25 C. in cyclohexane and an ethylene-propylene copolymer (53% ethylene) with an intrinsic viscosity of 6.7 dl./gm. at C. in Decalin. The results are shown in Table II in terms of hours required for complete dissolution.

TABLE II Hours required for complete dissolutionat room temperature West Texas crude oil Polymer/solvent cyclohexane Hydrogenated poly- 22 70.

Ethylene-propylene Not dissolved after Not dissolved after copolymers. 168 hours. 8 hours.

EXAMPLE III TABLE III Pipe I.D.: 6.125-inch Solvent: A West Texas crude oil Temperature: 76 F. Viscosity: 5.08 cs. Density: 0.823 grit/cm? Flow rate: 783 g.p.m.

Friction reduction Concentration (p.p.m.): (percent) 50 16 48 11 45 5 32. 2 27 Flow rate (g.p.m.): (percent) 15.14 26.3 23. 69 47.5 33.91 58.7 49.45 71.4

TABLE V Pipe I.D.: 1.25-inch Solvent: A West Texas crude oil Temperature: 77 F. Viscosity: 5.95 cs. Density: 0.827 gm./cm. Concentration: 10 ppm.

Friction reduction Flow rate (g.p.m.): (percent) 13.72 24.2 17.51 33.0 24.38 45.4 33.30 50.2

It will be understood that the hydrogenated polyisoprene additive should be soluble in the non-aqueous fluid being transferred. Examples of suitable fluids which are hydrocarbons and may be considered typical include hexane, pentane, cyclohexane, the isomers of octane, benzene, toluene and petroleum products such as crude oil, fuel oil and gasoline, as well as mixtures of such fluids.

We claim as our invention:

1. A composition for reducing fluid flow friction loss encountered in pipelines comprising a major amount of a liquid hydrocarbon having dispersed therein from about 1 ppm. to about 2,000 p.p.m. of hydrogenated homopolymer of isoprene having a viscosity'average molecular weight in the range of from about 1X10 to about 2x10".

References Cited UNITED STATES PATENTS 2,798,853 7/1957 Young et a1. 252-59 X 3,462,249 8/1969 Tunkel 44--62 3,493,000 2/1970 Canevari et a1. 137-13 3,682,187 8/1972 Seymour 137-13 2,028,349 1/ 1936 Heidelberg et a1. 25259 X 3,215,154 11/1965 White et a1. 44-62 OTHER REFERENCES Encylopedia of Polymer Science and TechnoL, vol. 7, 1967, pp. 795; 796 and 816.

W. H. CANNON, Primary Examiner US. Cl. X.R. 44-62; 137-13 

